1. Field of the Invention
This invention relates to image stabilizing photographic optical systems.
2. Description of the Related Art
In shooting the camera while riding on a moving motor vehicle such as a car or aircraft, vibrations propagates to the photographic system, thereby resulting in a blurred image at the focal plane. In this case, the distance the image shifts from the intended location in the picture frame increases as the focal length of the photographic system increases.
A method of avoiding such image shift has been proposed in the stabilized optical systems of, for example, Japanese Pat. Publications Nos. Sho 56-34847, 57-7414 and 57-7416.
The common method employed in these documents is that an optical member constituting part of the photographic system is freely suspended in space to generate a prism whose wedge angle varies with angular deviation of the camera from the intended line of sight so that the rays of light deflected by the prism provide a stationary image on the focal plane.
Meanwhile, U.S. patent applications Ser. Nos. 896,639, 116,668 and 116,541, now U.S. Pat. No. 4,844,602, disclose a technique that accidental motion of the photographic optical system is detected by utilizing, for example, an acceleration sensor. Responsive to the thus-obtained signal, an actuator oscillates a lens unit constituting part of the photographic system in a direction perpendicular to the optical axis to stabilize the image against such motion. As this actuator use may be made of a solenoid or a laminated assembly of piezoelectric elements.
It is also possible to use an image sensor such as CCD. Motion of the image formed on the CCD is analyzed through an electrical signal processing system. The thus-obtained signal may be used to obtain the stationary image at the focal plane.
In order that the photographic lens system is partly operated by means of the actuator in the manner described above to compensate for image movement to obtain the stationary image, the operating mechanisms are generally required to get a good responsiveness.
For this reason, the lens unit movable for image stabilization should be as far reduced in size and weight as possible, and the inertial mass be minimized. Further, tee relationship between the accidental displacement of the camera and the required amount of movement of that lens unit for compensating for the image movement is simplified with an advantage of shortening the computing time for conversion. Hence, the photographic lens system must be designed in such a way as to fulfill these requirements.
In addition thereto, because the movable lens unit when decentered produces decentering coma, decentering astigmatism, decentering chromatic aberrations and other decentering aberrations, it becomes difficult to preserve good optical performance against accidental displacement of the camera.